Electrical detector-amplifier circuits



` .lune 24, 1930. s, Y WHITE 1,165,473

ELECTRICAL DETECTOR AMPLIFIER CIRCUITS Filed Sept. l, 1925 Patented `lun'e 24, 1930 UNITED STATES" PATENT OFFICE SIDN'EY Y. WHITE,y OF NEWYORK, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS, TO RADIO CORPORATION OF AMERICA, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE ELECTRICAL DETECTOR-AMPLIFIER CIRCUITS `Appnmatiml med september While my invention relates generally to electrical detector-amplifier circuits, it refers particularly to three-electrode vacuum tubes employed in the dual capacity of detector and regenerative amplifier.

An object of my invention is to adjust the variable circuits of a three-electrode vacuum tube detector-ampliiier so that the degree of regeneration will remain constant, or vary in a pre-determined wayfthrough ut a wide range offrequencie's as the circui are varied.

Another object of my invention is to adjust the degree of regeneration so that the system will strongly amplify 'by regeneration throughout a wide range of frequencies Without breaking into oscillations when changing the circuits from one frequency to another; or, adjusting the system to be in oscillation throughout. a wide range of frequencies when changing from one fre uency to another. The one adjustment wi provide for the reception of modulated or damped high frequency currents without the usual annoyance of oscillations in changing from one wave length to another. The other adjustment will provide for the reception of continuous Waves by the heterodyne or beat method throughout a Wide range of frequencies without theannoyance of adjusting the system to be in the oscillating state for each changing of wave length.

A! further object of my invention is to take full advantage of the selectivity that may be had at any one of a wide range of frequencies? through producing regenerative amplification by a controlled reaction in the 'plate or output circuit of al three-electrode vacuum tube.

In my co-pending application, Serial Number 49,521 of August 11, 1925, I have lexplained how the reaction in the plate circuit of a three-electrode vacuum tube may be maintained constant while energy is being transferred over a wide range of frequencies to the input circuit of a succeeding vacuum tube.

My present invention relatesto a threeelectrode vacuum tube detector-amplifier or detector-oscillator from which the energy is 1,' 1925. serial No. 53,799.

abstracted in the form of low frequency effects corresponding to the detected modulations in the high frequency signals or the beat tones of the heterodyne, in case continuous waves are received. Y

My invention Will be best undestood by reference to the accompanying drawing in which Fig. 1 shows my invention applied to a radio receiver, and Fig. 2 is'an explanatory diagram. n

In Fig. 1, X is an antenna connected to ound Gr through a condenser C?)v and an lnductance L1, and may or may notinclude a condenser C1, depending upon the char-` acte'ristics of the antenna. High frequency energy is delivered to the vacuum tube VTl through the resonant circuit L2, C2, and C3, the coupling to the antenna being maintained constant, or varied in any pre-determined manner, with frequency through the combination inductive coupling between L1 and L2 and the capacity coupling G3, all more fully explained in the co-pending application heretofore referred to. The vacuum tube Y'Il is arranged to act as a straight ampli- Iier through having its grid connected to the negative side of the filament heating circuit. Y

The amplified high frequency currents in the output circuit of vacuum tube V'Il are transferred to the input Vcircuit of the detectorampliier, or detector-oscillator, VT2 through the variable circuit L2 C2 and C3, the coupling being maintained constant, or varied in any pre-determined manner, through the combination of the inductive coupling between L',L and L2 and the capacity coupling Cs, all as explained in my co-pending apphcation previously referred to. The radio frequency choke L3 provides a path forthe direct current supplied to the plate of vac- Auum tube V'Il. Vacuum tube VT2 is ar-` v lranged to act as a detector through having its grid'connected to the positive side of the filament supply line, and through provision of the well-known grid leak-stopping condenser combination GL.

As explained 'in `my co-pending application, there is an interelectrodal path in threeelectrode vacuum tubes suchas V'I2, through jwhich some of the amplified energy in the output circuitA escapes to the input circuit toreinforce the input circuit ener and I have explained that the amount an phase of energy which escapes to the input circuit determines .Whether or not the system will act as a regenerative amplifier, or as an oscillator.' l

' I have also explained that the amount of energy that escapes to the input circuit dem pends upon the reaction of the output circuit on the amplified energy. It is well-known that with the present day high amplification vacuum tubes the reaction due to attempting to tune the output circuit becomes so strong long before the output circuit is in resonance that the system breaks into oscillations, and

by the time near resonance is reached, the

system is a powerful oscillator. This is more clearly explained inthe diagram of Fig. 2,

in which the horizontal dimensions represent frequency of the signal current, and vertical dimensions represent reaction of the plate circuit to the selected current. Let 'it lbe,

assumed that the input circuit is tuned to and receiving signals of a frequency f shown in Fig. 2 by the dotted line. Assume that the output circuit is freel from resistance other than that inherent in the vacuum tube and necessary elements, and is capable of being 3o yariedfvwith the inputcircuit. The curve Y (of the figure shows in a general way the reaction had Ain' the output circuit as this circult 1s varied. The dotted line bb shows in a general way the value of the reaction inregenerative amplification and oscillation,y

the curve is very steep, so-that operating a vacuum tube near these points is an extremely critlcal and unstable condition. It is readlly apparent that, under the conditions outllned, no particular advantages are had in the'matter of selectivity through tuning the output circuit to produce regenerative amplification.

The curve Y can be forced belo the line bb into a form such as the dotted llne curve Q Y by introducing a substantial resistance in .65 line bb throughout a wide range of frequencircuit of VT2 through the inductive coupling between L1 and L2 and the capacity coupling Cs.

I have explained in my co-pending application' previously referred to how the capacity coupling decreases with increase of frequency, and how the inductive coupling increases with increasey of frequency, and how the combination may be adjusted to give out a wide range of frequencies; or, in other words, how thls coupled, var1able c1rcu1t may a coupling that will remain constant throughf be made to create a constant reaction through z the internal path of vacuum tube VT2. It is readily apparent that by adjusting the de, gree -or-looseness of this coupling which remainsl constant it may be maintained below or above the critical line bb: It will also be readily obvious tothose skilled in the art that the sharpness of the curve yZ of Fig. 2 provides a condition ofextreme `selectivity in the system I have outlined; v Telephones T are inserted in the path` provided for the direct current supply to the plate of vacuum tube VT2 to convert the low frequency `effects into sound, or these telephones may be substituted by a transformer T,'shown in dotted lines, leadingto one or more stages of audio frequency amplification. If the telephones T, or transformer l T, have a distributed' capacity in their windings too large to prevent high frequency currents from freely passing, the path lmay be re-inforced against passage of igh frequency currents by insertion 'of a suitable radio frequency choke L4.

The lines marked -l-A-B, -A and -l-B provide the usual system for heating the filaments of the vacuum tubes and energizing the plate circuits, and are thought to require -no' explanation.

While I have shown `the system as including a vacuum tube VTI for straight amplification, it is readily obvious that this tube may bev omitted, in which` event the *systeml I would be completed by connecting the antenna X in a suitable'manner Ato the input circuit of vacuum tube VT2. "f Although I have illustrated lmy invention in connection with a radio receiver, it is readily applicable to other forms of electrica l communication, and I do not intend that it be limited-'tothe system chosen forillustrative purposes.

Having fully described my invention, I claim:

1. The combination of. a three-electrode vacuum tube, a tunable high frequency input circuit, an output circuit, means operating said vacuum tube as a detector, a high frequency circuit, variable in consonance with said input circuit, means 'for coupling said high frequency circuit to said output circuit, the ratio of energy transfer of s aid coupling being substantially. less than unity, saidv coupling being adjusted to remain substantially constant as said second'circuit is varied, and means associated with said output cir` cuit for abstracting detected energy therefrom.

2. The combination of a three-electrode vacuum tube, a tunable high frequency input circuit, an output circuit, means for impressving high frequency currents modulated at lower frequency on sai'd input circuit, means operating said vacuum tube as adetector, a

vhigh frequency circuit variable in consonance with said input circuit coupled to saidoout- 'put circuit, means for "maintaining the rel action of said variablel circuit on said output circuit substantially A constant with frequency, including means for maintaining the coupling between said output circuit and said variable circuit substantially less than unity as said variable circuit is varied, as said second circuit is varied, and means associated with said output circuit foi` a stracting energy of saidlower frequency t erefrom.

3. The combination of a three-electrode vacuum tube, a tunable hi h frequency input circuit, an output circuit, means operating said vacuum tube as a detector, a high fre.- qency circuit variable in consonance with said input circuit, a cou ling comprising capacitively and inductive y reacting elements associating said variable circuit with said output circuit, said coupling being adjusted to remainsubstantiall constant as said 4variable circuit is varie in consonance with said n input circuit,.and means associated with said l' output circuit for abstracting detected energy therefrom. E

4. The combination of a three-electrode. vacuum tube, a tunable high frequency input circuit, an output circuit, mea'ns for impressinghigh frequency energy modulated at lower frequency on said vinput circuit, means operating said vacuum tube as' aldetector, -a-

j high frequency circuit variable in consonance ing said vacuum tu as a detector, a high freoperating said vacuum tu e as a detector, a-

high frequency circuit variable in consonance with said input'circuit coupled to said output circuit, meansfor maintaining the reaction of said variable circuit on said output circuit substantially constant withlfrequency including means for maintaining the coupling between said output circuit and variable circuit substantially constant as said variable circuit is varied, and means associated with said output circuit vfor abstracting detected energy therefrom.

7. The combination with a three-electrode vacuum tube having a tunable high frequency input circuit, an output circuit and means for operating said vacuum tube as a detector, of means for causing and controlling regeneration in said vacuum tube and circuits with variation of frequency comprising a high frequency circuit variable in consonance with said input circuit,a combined capacitive and inductive cou ling between said output and variable circuits, said coupling being adjusted to a predetermined degree of looseness and to remain substantially constant withfrequency, and means associated with said output circuit `for abstracting detected therefrom.

8. The combinationl with a three-electrode vacuum tube havinga tunable high frequency input circuit, an output circuit and means for energy operating saidtube as a detector, of means for maintaining the re enerative reaction throughthe interelectro al capacity of said tube constant with frequency over a wide range of frequencies comprisinga high fre-A 4 quenc circuit variable in consonance with said input circuit loosely coupled to said output circuit, meansfor maintaining said coupling substantially `constant asv said cou led circuit is'varied, and means associated). with said output circuit for abstractmg detected energy therefrom.

. In testimony whereof I aiix my signature.

SIDNEY Y. 

